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April 19, 2012

Picture of a Picture

The International Space Station in all its glory. Since I have been posting pictures of it lately I figured that I could not hurt to post a picture of what it actually looks like. Since I have never actually been to space to take a picture of it, this will have to do. This is a mural/picture of it on a wall at the Kennedy Space Center Visitor Complex. Below the mural are the flags of all the contributing nations. Quite the cooperative effort considering the past century of international relations...

To get an idea of the scale of the station, each of the bronze colored solar arrays is 39 feet wide and 115 feet long. They are huge. Interestingly, since there is still just a little bit of atmosphere at the altitude of the space station there is a tiny amount of atmospheric drag. This is what slows satellites down and the reason why they need to be boosted every so often to maintain their proper orbit. The solar arrays on the ISS are huge and produce a huge amount of drag.

They can be rotated around to change their orientation, and this is used by NASA to manage these effects. Often the station uses the night glider mode of operation whereby they orient the arrays in the direction of flight whenever they are in the earths shadow. This reduces the drag by a lot. They can also do that for entire orbits, but that reduces the amount of power they produce. Another use for them is to intentionally slow the station. This was used primarily for shuttle missions to reduce the altitude of the station to make it easier for the shuttle to reach.

Finally they can also be used as solar sails. They are all double sided. One is shiny and the other is not. The not shiny side can be turned toward the sun and just absorbs all the photons. If the shiny side is turned toward the sun, all the photons bounce off and transfer some of their momentum to the station, helping it maintain it speed and therefore altitude.

All of these effects are tiny, but they have a huge impact over months and years. Given that the cost of lifting a single kilogram of fuel to orbit runs at about $20,000, any reduction however small in the amount of fuel needed has a huge impact on the financial impact of the station.